As more and more consumers and businesses become mindful of the effect of vehicle emissions on the environment there has been a drive towards the development of electric powered vehicles, which use electrical power sources and electric motors as the heart of their drive train. A battery-powered vehicle will emit no harmful carbon dioxide emissions and can be charged quickly and easily by connecting it to a mains power supply.
To date a limitation of such vehicles has been the amount of energy that can be stored in the electric power source that in turn limits the range that the vehicle can travel between recharging. Advances in battery technology have meant that more energy can be stored in smaller, and hence lighter, power sources and the technology is now at the stage where a vehicle with a usable range of 50 miles or more and an acceptable top speed of, say 50 mph or so, can be produced.
There is still a need to reduce the battery unit weight to a minimum, especially for a commercial vehicle such as a delivery van, because less battery weight means that a greater payload can be carried. It is therefore important to be able to minimise wherever possible the battery drain. At present most attempts to control the battery drain during use of the vehicle have focused on improving the efficiency of the electric motor and reducing rolling resistance/drag of the vehicle. The applicants have appreciated that an effective battery power control strategy would be desirable.
A further problem appreciated by the applicant is that the security of a delivery vehicle, and to a lesser extent other vehicle types, is paramount as the driver is continually getting in and out of the vehicle. Home deliveries are increasing, in particular as a result of the growth in shopping for good on the Internet. A delivery driver may park a vehicle at a delivery address and then quickly take the goods to the address before returning. It is all too easy for the driver to forget, or choose not, to turn off the vehicle when making a delivery, which makes it vulnerable to an opportunist thief. In any event, the vehicle may be vulnerable to theft.
One well established solution to the problem of vehicle security is to fit the vehicle with an immobiliser. On a conventional petrol or diesel engined vehicle, this will isolate an electrical circuit which is needed to start the vehicle. For example, it may isolate the starter motor or, in a more sophisticated arrangement, send an instruction to the engine management unit not to provide fuel to the engine.
Whilst such immobilisers work well on petrol/diesel cars, they do not function well on electric vehicles due to the relatively long period of time it takes the battery and other electrical systems to move from a powered down state to a state in which the vehicle is ready to drive. On a petrol/diesel vehicle there is little need to power down items as battery life is not so great an issue, range not being limited by battery capacity but by the amount of fuel on board. The battery needs to be checked and the vehicle needs to perform diagnostics on the battery to ensure there is sufficient power and that the battery is safe to use. Only then can the switch means that selectively isolates the battery contacts, typically mechanical battery contactors, be closed to connect the HV electrical items to the battery. This time delay may prove irritating to a delivery driver who is repeatedly getting in and out of the vehicle if the immobiliser activates each time. Leaving things powered up all the time, on the other hand, will simply drain the battery reducing the range of the vehicle and leave it vulnerable to theft. Also, repeated opening and closing of the contactors can cause premature wear due to arcing and the like.